Luminaires with automated and remotely controllable functionality are well known in the entertainment and architectural lighting markets. Such products are commonly used in theatres, television studios, concerts, theme parks, night clubs and other venues. As well as usually providing control over the pan and tilt functions of the luminaire allowing the operator to control the direction the luminaire is pointing a typical product will also often provide control over the color of the emitted light beam. Typically this color control is done via the movement of color wheels, flags or other similar device containing colored filters. Very often these colored filters are gradated from one end to the other with an increasing density of the color filter or increasing saturation of the color that is being filtered. Typically, in these systems the light beam only passes through a portion of the filter. By moving the gradated filter so that different portions of the filter are placed in the path of the light beam the color saturation of the light beam can be varied.
FIG. 1 shows a filter of this kind with a gradated saw-tooth color coating 101. Filter 101 is progressively moved from into the path of the light beam cross section 102 in the light train of the luminaire anywhere from position a to d. As the movement continues from position a to d an increasing portion of the light beam cross section 102 passing through the color modulating portions 103 (shown as the hatched area in FIG. 1) of filter 101 and thus the resultant light becomes more and more color saturated. When the filter 101 is in position d the entire cross section 102 passes through the color modulating portions 103 the filter 101 and the color saturation is complete for that filter.
Although a rectangular filter 101 is shown here with linear motion it is also common for these devices to use circular filters with a rotary motion.
A single filter 101 is illustrated here, however in practice multiple color filters with the same or different color modulating properties may be used so that the light passes through or bypasses each filter in turn. Such an arrangement creates a subtractive color mixing system where the color of the output light is defined by the combination and position of all the filters in use. The products manufactured by Robe Show Lighting such as the ColorSpot 1200E are typical of the art.
In typical color modulation systems a combination of two or more of these variable saturation mechanisms, one after the other in the optical train with different colored filters to provide a variable color mixing system across a color gamut.
It is very common to use three color filters, one each of Cyan, Magenta and Yellow each of variable saturation. Combining these in varying subtractive mixes allows the production of a very wide gamut of colors.
Lighting designers and other users of such products often have a desire to change colors very rapidly. Quickly enough that the audience does not perceive the change happening and instead sees it as an instantaneous event. The speed of these changes are typically limited by the mechanical design and construction of the mechanism used for the color change.
FIG. 2 illustrates a typical multiparameter automated luminaire system 10. These systems typically include a plurality of multiparameter automated luminaires 12 which typically each contain on-board a light source (not shown), light modulation devices, electric motors coupled to mechanical drives systems and control electronics (not shown). In addition to being connected to mains power either directly or through a power distribution system (not shown), each luminaire is connected is series or in parallel to data link 14 to one or more control desks 16. The luminaire system is typically controlled by an operator through the control desk 15.
FIG. 3 illustrates different levels of control 20 of a parameter of the light emitted from a luminaire. In this example the levels are illustrated for one parameter: color. The first level of control 22 is the user who decides what he wants and inputs information into the control desk through typical through computer human user interface(s) 24. The control desk hardware and software then processes the information 26 and sends a control signal to the luminaire via the data link 14. The control signal is received and recognized by the luminaire's on-board electronics 28. The onboard electronics typically includes a motor driver 30 for the color motor (not shown). The motor driver 30 converts a control signal into electrical signals which drive the movement of the color motor. The color motor is part of the color mechanical drive 32. When the motor moves it drives the mechanical drive 32 to move the mechanical components which cause the light beam emanating from the luminaire to change color.
In some systems it may be possible that the motor driver 30 is in the control desk rather than in the luminaire 12 and the electrical signals which drive the motor are transmitted via an electrical link directly to the luminaire. It is also possible that the motor driver is integrated into the main processing within the luminaire 12. While many communications linkages are possible, most typically, lighting control desks communicate with the luminaire through a serial data link; most commonly using an industry standard RS485 based serial protocol called commonly referred to as DMX-512.
Particular problems inhibiting and limiting the speed, accuracy and repeatability of the movements of the color system of an automated luminaire are the mechanical stiffness and inertia of the color mechanism and its drive system. It is typical in such products to use a single motor or a pair of motors connected to the driven color change mechanism through either a belt drive or through a direct geared system. As well as the stated problems in both cases there is inevitably an amount of backlash or slippage or shifting which induces hysteresis in the system. Such hysteresis would manifest itself as an undesirable and visible color shift in the light output.
Various prior art systems have offered solutions to these problems. One solution to reducing the time needed for a color change is to reduce the length of travel of the mechanism. However compressing the length of the graded filter (component 101 in FIG. 1) may have the unintended side effect of making the light field uneven as the color saturation density on one side of the aperture may be significantly different than on the other.
There is a need for a color change system which can provide rapid and accurate movement without backlash and hysteresis.